The tests only appear to last briefly (Reddit user Pixel3aXL saw it come and go within hours) and don’t affect the homepage, but they work in third-party browsers like Firefox.
The look is the same, at least. If you get the test, you’ll see a dark gray background with a white Google logo and blue buttons.
It’s not certain when (or if) Google will expand the test to more people. It won’t be surprising if there’s a wider rollout in the months ahead, though.
Both macOS and Windows 10 have had dark themes for a while, and Chrome itself supports dark modes for individual websites.
A dark mode desktop search page would save you from searing your eyes during those late-night computing sessions, at least this is a plus for everyone.